# I Bullet clusters & CMB accoustic peaks dark matter

1. Dec 26, 2016

### kodama

is it possible the dark matter in bullet clusters & CMB accoustic peaks were the result of black holes, originally from baryonic matter, but galaxy rotation curves are MOND.

So MOND + dark matter as black holes from baryon, not dark matter particles

2. Dec 26, 2016

### Staff: Mentor

I don't believe so. That much mass would require an enormous number of black holes. Far more than what would be reasonably expected to form. There should also be accretion disks that should be observable in at least some cases, but I don't think we see any evidence of these.

3. Dec 26, 2016

### kodama

MOND does reduce the amount of dark matter that needs to be invoked. in the case of bullet clusters the remaining dark matter could be black holes, or many black holes.

as for cmb accoustic peaks what about neutrinos which is known to exist

4. Dec 26, 2016

### Staff: Mentor

That's still a lot of black holes. The question would then be why there is so much mass tied up in black holes but no evidence for them.

5. Dec 26, 2016

### kodama

evidence is in the gravitational lensing in bullet cluster

6. Dec 26, 2016

### Staff: Mentor

I'm only aware of large-scale lensing, nothing that would suggest black holes. Do you have a reference that says otherwise?

7. Dec 26, 2016

### kodama

this paper states standard cold dark matter doesn't work for bullet clusters, and then verlinde's version of mond predicts more gravitational lensing from baryonic matter alone than GR

Bullet Cluster: A Challenge to LCDM Cosmology
Jounghun Lee (Seoul Nat'l U.), Eiichiro Komatsu (U.Texas at Austin)
(Submitted on 4 Mar 2010 (v1), last revised 22 May 2010 (this version, v2))
To quantify how rare the bullet-cluster-like high-velocity merging systems are in the standard LCDM cosmology, we use a large-volume 27 (Gpc/h)^3 MICE simulation to calculate the distribution of infall velocities of subclusters around massive main clusters. The infall-velocity distribution is given at (1-3)R_{200} of the main cluster (where R_{200} is similar to the virial radius), and thus it gives the distribution of realistic initial velocities of subclusters just before collision. These velocities can be compared with the initial velocities used by the non-cosmological hydrodynamical simulations of 1E0657-56 in the literature. The latest parameter search carried out recently by Mastropietro and Burkert showed that the initial velocity of 3000 km/s at about 2R_{200} is required to explain the observed shock velocity, X-ray brightness ratio of the main and subcluster, and displacement of the X-ray peaks from the mass peaks. We show that such a high infall velocity at 2R_{200} is incompatible with the prediction of a LCDM model: the probability of finding 3000 km/s in (2-3)R_{200} is between 3.3X10^{-11} and 3.6X10^{-9}. It is concluded that the existence of 1E0657-56 is incompatible with the prediction of a LCDM model, unless a lower infall velocity solution for 1E0657-56 with < 1800 km/s at 2R_{200} is found.
Comments: accepted for publication in ApJ, light-cone effect discussed, minor typos corrected, 22 pages, 6 figures, 3 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Journal reference: Astrophysical Journal 718 (2010) 60-65
DOI: 10.1088/0004-637X/718/1/60
Report number: TCC-009-10
Cite as: arXiv:1003.0939 [astro-ph.CO]

8. Dec 26, 2016

### Staff: Mentor

Unless I'm mistaken, nothing in that paper says anything about black holes, which is what I was asking for a reference to.

9. Dec 26, 2016

### kodama

when it comes to large scale lensing, 1 erik verlinde paper has received considerable press and offers new equations and

2 the following paper shows that Verlinde MOND-like version of gravity can reproduce darkmatter like lensing as it makes gravity stronger over large distances.

no need to modify the SM. no need to introduce new particles

so using a MOND-like gravity like Verlinde can explain most of the lensing seen in bullet clusters, and whatever is residual can be explained as black holes.

Emergent Gravity and the Dark Universe
Erik P. Verlinde
(Submitted on 7 Nov 2016 (v1), last revised 8 Nov 2016 (this version, v2))
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional dark' gravitational force describing the elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a_0 =cH_0, and provide evidence for the fact that this additional `dark gravity~force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
Cite as: arXiv:1611.02269 [hep-th]

First test of Verlinde's theory of Emergent Gravity using Weak Gravitational Lensing measurements
Margot M. Brouwer, Manus R. Visser, Andrej Dvornik, Henk Hoekstra, Konrad Kuijken, Edwin A. Valentijn, Maciej Bilicki, Chris Blake, Sarah Brough, Hugo Buddelmeijer, Thomas Erben, Catherine Heymans, Hendrik Hildebrandt, Benne W. Holwerda, Andrew M. Hopkins, Dominik Klaes, Jochen Liske, Jon Loveday, John McFarland, Reiko Nakajima, Cristóbal Sifón, Edward N. Taylor
(Submitted on 9 Dec 2016 (v1), last revised 19 Dec 2016 (this version, v2))
Verlinde (2016) proposed that the observed excess gravity in galaxies and clusters is the consequence of Emergent Gravity (EG). In this theory the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the excess gravity (described as an apparent dark matter density) in terms of the baryonic mass distribution and the Hubble parameter. In this work we present the first test of EG using weak gravitational lensing, within the regime of validity of the current model. Although there is no direct description of lensing and cosmology in EG yet, we can make a reasonable estimate of the expected lensing signal of low redshift galaxies by assuming a background LambdaCDM cosmology. We measure the (apparent) average surface mass density profiles of 33,613 isolated central galaxies, and compare them to those predicted by EG based on the galaxies' baryonic masses. To this end we employ the ~180 square degrees overlap of the Kilo-Degree Survey (KiDS) with the spectroscopic Galaxy And Mass Assembly (GAMA) survey. We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.
Comments: 14 pages, 3 figures. Accepted for publication in MNRAS. Added references for section 1 and 6
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
DOI: 10.1093/mnras/stw3192
Cite as: arXiv:1612.03034 [astro-ph.CO]

10. Dec 26, 2016

### Staff: Mentor

This is the last time I'll ask. Please provide a reference supporting this claim, not one for a MOND theory.